Electrical devices with frictionless flexible contacts



April 1968 J. w. FORREST 3,

ELECTRICAL DEVICES WITH FRICTIONLESS FLEXIBLE CONTACTS Filed April 26,1967 I 2 Sheets-Sheet L INVENTOR. JOHN W FORREST BY @ZflflW ATTORNEY Aril 9, 1968 J. w. FORREST ELECTRICAL DEVICES WITH FRICTIONLESS FLEXIBLECONTACTS Filed April 26, 1967 2 Sheets-Sheet FIG. 4

INVENTOR. JOHN W. FORREST ATTORNEY United States Patent 3,377,604ELECTRICAL DEVICES WITH FRICTIONLESS FLEXIBLE CONTACTS John W. Forrest,West Acton, Mass., assignor to Acton Laboratories, Inc., Acton, Mass, acorporation of Massachusetts Filed Apr. 26, 1967, Ser. No. 633,999 14Claims. (Cl. 338154) ABSTRACT OF THE DISCLOSURE This patentspecification describes improvements in devices of the type shown in US.Patents 2,862,088, 3,070,- 768, 3,170,047 and 3,274,350 whichessentially comprise a rotating depressor which runs over a flexuralcontact diaphragm and urges the latter to successively engage a seriesof switch contacts or successive portions of an electrical resistor. Theinvention involves changes in how the diaphragm is supported and how thedepressor is disposed with respect to the diaphragm, as well as animproved mode of assembling the various parts so as to maximizediaphragm life, stabilize the output signal, and facilitate disassemblyfor inspection and repair.

This invention relates to encapsulated rotary electrical control devicesand more particularly to encapsulated rota-ry switches andpotentiometers.

Field of invention Prior art The most pertinent prior art known toapplicant consists of US. Patents 2,862,088, 3,070,768, 3,170,047 and3,274,350, and the references cited therein. The chief limitation ofprior encapsulated switches and potentiometers is the difficulty ofmaintaining quality and meeting operational specifications whenmanufacturing units in production quantities. Although it has beenpossible to build units that perform satisfactorily over a large numberof operating cycles, such success has been sporadic and unpredictable.The chief problem that has persisted is inconsistent performance of thediaphragm, with some diaphragms functioning satisfactorily for as muchas 30 million operating cycles of the depressor but more failing toperform to specifications after 10-15 million cycles. In some cases thedeterioration in performance has involved rupture or cracking of thediaphragm along the line of contact by the depressor, but in other casesthe deterioration has been manifested by marked decreases in the signalto noise ratio and variations in output signal quality with changes inambient temperature. It has been discovered that this problem ofdiaphragm performance is attributable to a variety of factors, includingthe way in which the diaphragm is mounted, misalignment of parts anddifferences between the thermal coefficient of expansion of the metallayer of the diaphragm and that of the disc carrying the switch segmentsor resistor element. Another problem is that the amount of torquerequired to rotate the depressor tends to change during extendedoperation. Other problems are improper positioning and clamping of thedis-c carrying the switch segments or resistor element. If the disc is3,377,604 Patented Apr. 9, 1968 not secured tight enough and hence canmove, noise will occur in the output signal. On the other hand if thedisc is secured so tightly as to be distorted, the contact made by thediaphragm with the switch segments or the resistor element may varysufficiently to produce undesired variation in the output signal. Theseand other problems have been complicated by the fact that prior designswere not adapted to production control permitting detection of defectsand replacement of defective parts at different stages of assembly.

Summary of invention The general object of this invention is to providenew and improved devices of the character described that overcome theproblems previously existent in the prior art. More specific objects ofthe invention are to provide modifications over the prior art thatminimize the contact area and diaphragm stress, reduce contact laminatewear, assure constant torque over extended use, facilitate rnounting ofthe switch and resistor discs without'physically distorting them,simplify shaft alignment and loading of bearings, minimize noise andfluctuation in the output signal, and permit detection of defects atdifferent stages of assembly.

These and other objects are achieved by providing an electrical controldevice consisting of an annular disc carrying a circular array of spacedswitch segments or a circular resistor element, an annular laminatedcontact diaphragm consisting of an outer layer of a hard fatigueresistant spring alloy and an inner layer of a low electrical resistancemetal, a pair of standoff rings separating the disc and diaphragm attheir inner and outer edges with only one of said standoff rings securedto both the disc and diaphragm, an insulated depressor mounted on arotatable shaft and positioned to slide on and press the diaphragmagainst the switch segments or resistor element, and bearing means forrotatably supporting the shaft. The device also includes means forclamping the disc under controlled pressure, and means for adjustablyloading the bearings. The standoff rings are made of a resilientmaterial that provides dimensional stability yet yields sufficiently tominimize diaphragm strain.

Other objects and advantages of the invention are believed to be readilyapparent from the following detailed description which is to beconsidered together with the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of a commutator switch embodyingthe invention;

FIG. 2 is an end view of the same device looking from right to left inFIG. 1;

FIG. 3 is a fragmentary top view of the switch disc and contactdiaphragm, with certain parts broken away for convenience ofillustration; and

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

Turning now to FIG. 1, there is a commutator switch comprising acylindrical housing 2 having an end wall 4 provided with a centrallylocated hole 6 to accommodate a shaft 8 on which is mounted a depressorassembly indicated generally at 10 that coacts with a switch assemblyindicated generally at 12. The opposite end of housing 2 is formedwithout an end wall but is closed off by a cover 14.

Referring now'to FIGS. 3 and 4, the switch assembly comprises (a) arigid annular non-conductive switch disc 16 preferably made of epoxyresin reinforced with glass fibers and having a circular array of spacedswitch segments 18 on one face thereof, (b) a flexural annular contactdiaphragm identified generally at 20 that overlies the said one face ofthe switch disc, and (c) a pair of concentric standoff rings 22 and 24disposed between the 3 switch disc and the contact diaphragm andfunctioning to support the latter in spaced relation to the switchsegments 13. The switch segments are plated onto the disc 16. and aremade of a conductive metal or metal alloy. This preferred embodiment isadapted for multiplexing digital information emanating from threedifferent sources. Accordingly the switch segments 18 are coupledtogether in three discrete groups 18A, 18B and 18C, with successivemembers of one group separated by a member of each of the other groups.More specifically, switch segments 18A are connected by a continuousribbon 26 of conductive metal that encircles and is coplanar with thearray of switch segments, switch segments 18B are connected by asecondribbon of conductive metal 28 that is coplanar with and runs along theinside of the array, and switch segments 18C are connected by a thirdribbon 30 that is concealed within switch disc 16 and follows a zig-zagpattern between segments. Ribbon 30 is connected to switch segments 18Cby short vertical conductive members 32. Four different conductive metaleyelets 34, 36, 38 and 40 are attached to the switch disc near itscenter. Switch segments 18A are electrically connected to eyelet 34 by ashort plated metal strip 42, switch segments 18B are connected to eyelet36 by a second plated metal strip 44, and switch segments 18C areconnected to eyelet 38 by a third plated metal strip 46. The fourtheyelet 40 is reserved for connection to the contact diaphragm.

The flexural contact diaphragm is of laminated metal construction andcomprises an outer layer 50 formed of a hard, fatigue resistant springmetal alloy whose physical properties are retained to a satisfactorydegree over a wide temperature range, e.g., from sub-zero temperaturesup to about 500 F. A number of cobalt-based alloys meet theserequirements, but I prefer to employ the alloy Havar manufactured byHamilton Watch Company, Precision Metals Division, Lancaster, Pa., orElgiloy sold by the Elgin National Watch Co. The contact diaphragm alsocomprises an inner layer 52 of a conductive metal, preferably gold,which is secured to the outer layer by an intermediate layer 54 of ametal such as nickel which can bond readily to the inner and outerlayers. The outer spring metal layer preferably has a thickness in therange of from about .0008 to about .001 inch, while the nickel and goldeach are plated on in layers measuring about 50 10 inch. The laminate isformed free of wrinkles, depressions and scratches. The foregoinglaminated construction is not novel with me but is taught by U.S. PatentNo. 3,274,350 issued Sept. 20, 1966, 'to E. H. Mongeau for FrictionlessContact Construction for Electrical Devices. However it is to be notedthat the Mongeau patent teaches the use of a flexible depressor trackingring made of Mylar or similar material that is attached to the outersurface of the cobalt alloy layer and serves to insulate the depressorfrom the contact diaphragm. In the practice of my invention as hereindescribed and illustrated I deliberately omit the flexible insulatingtracking ring and instead permit the depressor to directly engage thecontact diaphragm. The purpose of this departure from the teaching ofMongeau is explained below.

I have determined that the standoff rings 22 and 24 must havedimensional stability yet be resilient. I also have found that improvedresults are achieved if the inner standoff ring 22 is secured to boththe contact diaphragm and the switch disc while the outer standoff ring24 is secured to only the contact diaphragm. This arrangement appears tobe particularly advantageous for small diameter commutators, e.g.,commutators having an outside diameter of 1-l' /2 inches. I have furtherdetermined that best results are obtained if the inner standoff ring ismade of a material having a durometer of about 40-50 and if the outerstandoff ring is made of kraft paper. The requirements for the innerstandoff ring are met if it is made of single ply Scotchweld #583adhesive tape (a product of Minnesota Mining and Manufacturing Co.)measuring about 2 l0 inch thick. This tape is a flexible solids dry filmadhesive composed of a synthetic elastomer and a combination ofthermosetting and thermoplastic resins. In its uncured state, i.e.,before heat is applied, the tape has a tensile strength of 3.2 lbs. perinch of width and is capable of minimum elongation of 300%. This tape isadapted to adhere to a variety of materials when subjected to heat andpressure.

In practice the inner standoff ring 22 is secured to the contactdiaphragm by application of heat and pressure. Then the kraft ring 24(measuring about 0.002 inch thick) is cemented to the diaphragm usingPhiobond cement. Then the diaphragm is placed over the switch disc withthe standoff rings located concentrically with the circular array ofswitch segments and the inner standoff ring is secured to the switchdisc by use of heat and pressure. Firm adherence of the Scotchweld ring22 to switch disc 16 and/or diaphragm 20 is achieved by applyingpressure of about 100 psi. at a temperature of about220- 240 F. forabout one hour.

The diaphragm is formed with a tab 58 on its inner edge. After thediaphragm is secured to the switch disc, a flexible lead 60 is solderedto tab 58 and also to the fourth eyelet 40. The encapsulated switchassembly 12 is completed by four insulated flexible wire leads 62 whichare inserted into and soldered to the eyelets 3640.

Referring now to FIG. 1, the shaft 8 is supported by a roller bearing 66whose inner race is secured to the shaft and whose outer race is sizedto make a snug fit in the hole 6 provided in the end wall 4 of thehousing, The outer race of the bearing is provided with a flange 68 thatengages the inner surface of the end wall 4 and shaft 8 is formed withan annular flange 70 that engages the inner race of the bearing.

The depressor assembly 10 comprises two metal plates 72 and 74 betweenwhich is sandwiched a flat spring metal arm 76 (preferably formed ofspring steel or beryllium copper). Plates 72 and 74 and arm 76 areformed with holes of identical size to accommodate a sleeve 78 formed ofa sturdy insulating material, preferably a plastic such as Delrin ornylon. Sleeve 78 is cemented to shaft 8 and, although not shown, it isto be understood that arm 76 and plates '72 and 74 are interlocked withsleeve 78 so as to rotate therewith. Such interlocking may be achievedby a keying or tongue and groove arrangement. The two plates and arm 76are clamped together by one or more rivets 80. Arm 76 projects radiallyof shaft 8 and attached to one projecting end thereof is a small shaft82 carrying a miniature roller bearing 84 which functions as a depressorfor the contact diaphragm. The outer race of bearing 84 is beveled so toprovide a rounded surface as shown at 86. It is to be noted that the armhas a length such that the roller bearing depressor 84 is not locatedmidway between the two standoff rings but instead is positioned so thatits circular line of contact with the diaphragm subdivides the latterinto two concentric annular portions of approximately equal area. Ineffect the depressor tracks along a line of minimum strain.

Referring again to FIGS. 1 and 2, the cover 14 has four evenly spacedthreaded holes into which are screwed four insulated terminals 90, 92,94 and 96 of conventional construction. The four flexible leads 62 whichare attached to the eyelets in the switch disc are connected to theseterminals. The cover also has a centrally located hole 98 in which ispositioned a roller bearing 100, The outer race of bearing 100 is sizedto fit snugly in hole 98 while its inner race is secured to shaft 8. Thelatter is provided with a circumferential groove into which is snapped aC-shaped retaining ring 102 which engages the inner race of hearing 100.The outer race of the bearing is engaged by a cup-shaped metal spacer104 which in turn is engaged by a Belleville spring washer 106 and oneor more shims or spacers 108. The latter are captivated by anotherC-shaped retaining ring 110 that snaps into a suitable groove formed inthe cover around hole 98. The encapsulated switch assembly 12 is heldagainst shoulder 64 by the cover acting through a resilient O-ring 112.The cover is secured to the housing by one or more screws 114.

Operation of the illustrated commutator is straightforward. Assume that(a) terminals 90, 92 and 94 are connected internally to the three groupsof switch segments 18A, 18B and 18C and terminal 96 is connectedinternally to contact diaphragm 20 in the manner described above; (b)terminals 90, 92 and 94- are connected externally to three differentsignal channels, e.g. channels generating information signals, andterminal 96 is connected externally to a signal processing system, e.g.a telemetering transmitter; and (c) shaft 8 is connected to and drivenby an electric motor. The depressor assembly 10 will rotate with respectto switch assembly 12 and as it does, the depressor roller 84 will presssuccessive portions of the contact diaphragm into contact withsuccessive switch segments, with the result that the three signalchannels are alternately switched into and out of connection with the Hsignal processing system that is connected to terminal 96.

Although not illustrated, it is to be understood that the invention alsois applicable to rotary potentiometers, as is the case with theinvention described and claimed in US. Patent No. 3,274,350 mentionedabove. This alternative mode of practicing the invention is notillustrated for the purposes of brevity of this specification and alsobecause it is believed to be clear to persons skilled in the art.Suffice it to say that in making potentiometers the switch segments aresupplanted by a resistor element as described in the aforementionedPatent 3,274,350 and also in US. Patent No. 2,862,089. Of course, in thecase of a potentiometer, only three eyelets like those shown at 3440 inFIG. 3 (and also only three insulated terminals like those shown at9096) are required, two connected to the ends of the resistor elementand the third connected to the contact diaphragm.

Commutators and potentiometers embodying the invention hereinexemplified and described offer many important advantages. For example,assembly is facilitated. Except as explained below, the variouscomponents are assembled in the order in which they occur looking fromleft to right in FIG. 1. The bearing 62 and the depressor assembly aremounted on shaft 8 before it is inserted into the case. The leads 62 aresuificiently long to permit them to be connected to the terminals 90-96before or after the switch assembly is inserted. This mode of assemblyalso facilitates disassembly of the device to the extent necessary tocheck for malfunctioning, electrical shorts, etc.

Another important advantage is the manner in which the switch assembly12 is held in place. The clamping force exerted by shoulder 64 and thecover 14 acting through the resilient O-ring 112 is suflicientlypositive to prevent movement of the switch assembly, yet is limitedsuificiently by virtue of compression of the O-ring to avoid distortionof the switch assembly.

A further advantage results from the mode of mounting the shaft 8.Unlike previous designs, it is a relatively easy task to adjust theloading on the shaft bearings. This involves varying the number and/orthicknesses of the shims 108, and may be accomplished without removingthe cover. It is to be noted also that the use of through bearing holes6 and 98 also facilitates checking for shaft alignment.

Still another advantage results from the fact that the depressordirectly engages the spring metal layer 50 of the contact diaphragminstead of running on a tracking ring made of Mylar or similar materialwhich is softer than layer 50. I discovered that relatively softmaterials such as Mylar tend to undergo physical changes, e.g. coldflow, even under the realtively light pressure required to be exerted bythe depressor to press the contact diaphragm against the switchsegments. These physical changes are felt as variations in the torquerequired to rotate the depressor. No such result occurs when thetracking ring is III eliminated and the depressor made to engage themetal laminate in the manner described herein. Of course thismodification involves insulating the depressor assembly from the shaftto avoid short circuiting.

The most notable advantages of the invention are substantial reducton innoise, extended diaphragm life (between 30 and million cycles), andelimination of fluctuations in the output signal throughout the dutycycle over a wide temperature range. The reduction in noise isattributable to the combination of diaphragm flexing and yielding of thestandoff ringsv The extended life is attributable to the distortion-freeclamping arrangement, the resilient standoff rings (including the factthat only one ring is secured to the rigid switch disc), and theposition of the depressor with respect to the diaphragmf The resiliencyof the standoff rings (together with the fact that only one ring issecured to the switch disc) stabilizes the output signal despitedisproportionate expansion or contraction of the diaphragm and theswitch disc due to changes in ambient temperature. The standoff ringscompress to the extent desired to permit pressing the diaphragm againstthe switch disc, yet are dimensionally stable to the degree necessary tomaintain a minimum gap between the two where relieved of the depressorpressure. The standoff rings have no tendency to set in compressedcondition at elevated temperatures e.g., 96 C. and remain resilient evenat temperature as low as C.

A further incidental advantage resides in the fact that the tab 58 ofthe contact diaphragm is not directly secured to the eyelet 40 butinstead is connected thereto by the flexible service lead 60. Idiscovered that cementing the tab to the switch disc (as is shown in US.Patent No. 3,274,350) has a limiting effect on the flexibility of thecontact diaphragm. This effect is avoided by using the service lead 60since this arrangement allows the tab freedom to move up and down as thediaphragm is flexed.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsspecifically described or illustrated, and that within the scope of theappended claims, it may be practiced otherwise than as specificallydescribed or illustrated.

I claim:

1. An electrical device comprising a housing; a contact assembly mountedwithin said housing, said contact assembly comprising (1) a rigidannular disc having at least one electrically conductive element on oneface thereof, (2) a flexural annular conductive contact diaphragmoverlying said disc in parallel relation to said conductive element, (3)a first resilient standoff ring disposed between said disc and saiddiaphragm adjacent the inner edges thereof, said first ring secured tosaid disc and also to said diaphragm, and (4) a second resilientstandoff ring disposed between said disc and said diaphragm adjacent theouter edges thereof, said second ring secured only to said diaphragm,said rings supporting said diaphragm in spaced relation to said disc;depressor means pressing a portion of said diaphragm into contact withsaid at least one conductive element, and drive means for moving saiddepressor means along said diaphragm so as to cause said depressor meansto press successive portions of said diaphragm into contact withsuccessive portions of said conductive element.

2. An electrical device as defined by claim 1 wherein said lastmentioned drive means is adapted to move said depressor means in acircular path along said contact diaphragm, and further wherein saiddepressor means is dis posed so as to contact said diaphragm along aline that is closer to said second ring than said first ring.

3. An electrical device as defined by claim 1 wherein said diaphragm isprovided with a tab on its inner edge and said disc is provided with atleast two conductive terminal members, and further including meanscoupling one of said terminal members to said at least one conductiveelement and a flexible insulated lead attached at one end 7 to said taband at the other end to another of said terminal members.

4. An, electrical device as defined by claim 1 wherein said depressorcomprises a roller whose peripheral surface is bevelled to reduce thearea of its contact with ;he diaphragm.

5. An electrical device as defined by claim 1 wherein said diaphragm isof laminated construction and comprises a thin conductive inner layerfacing said disc and an outer layer made of a conductive resilient hardalloy, and further wherein said depressor means is insulated so as toprevent electrical shorting through said drive means.

6. A device as defined by claim 1 wherein said disc has a plurality ofspaced conductive elements disposed in a circular array on said one facethereof, and said drive means is adapted to move said depressor means ina circular path along said contact diaphragm so as to cause successiveportions of said diaphragm to be flexed into and out of contact withsuccessive ones of said conductive elements.

7. A device as defined by claim 1 wherein said housing is formed with anopen end and also an interior annular shoulder which is engaged by theouter edge portion of said one face of said disc, and further whereinsaid device includes a resilient member engaging the opposite face ofsaid disc and a cover member secured in said open end and pressing saidresilient member against said disc so that said contact assembly isclamped between said shoulder and said resilient member.

8. A device as defined by claim "7 wherein said resilient member is anO-ring.

' '9. An electrical device comprising a housing; a contact assemblymounted within said housing, said contact assembly comprising (1) astiff annular disc having at least one electrically conductive elementon one face thereof, (2) a flexural annular'contact diaphragm overlyingsaid disc in parallel relation thereto, and (3) first and secondstandoff rings interposed between said diaphragm and said disc at theinner and outer edges respectively thereof, said standoff ringssupporting said diaphragm in close spaced relation to said disc; a shaftextending axially through the open center of said contact assembly;means rotatably supporting said'shaft; and a depressor assembly securedto said shaft, said depressor assembly including a depressor memberspaced radially of said shaft and adapted to press successive portionsof said diaphragm into contact with successive portions of said at leastone conductive element as said shaft is rotated, said depressor memberlocated so that its movement along said diaphragm follows a circularpath that is located closer to said sec-nd standoff ring than said firststandoff ring.

10. An electrical device as defined by claim 9 wherein the unsupportedsurface area of said diaphragm between said first standoff ring and saidcircular path is approximately equal to the unsupported area of saiddiaphragm between said second standoff ring and said circular path.

11. An electrical device comprising a housing open at one end andprovided with an end wall at its opposite end, said housing having aninterior annular shoulder located intermediate its ends; a contactassembly within said housing, said contact assembly comprising a stiffannular disc having the 'outermarginal portion of one face thereof inengagement with said shoulder, at least one electrically conductiveelement on said one face, and a flexural annular contact diaphragmsecured to said one face in overlying parallel spaced relation to saidat least one conductive element; a shaft; first bearing means mounted insaid end wall; a first portion of said shaft rotatably supported by saidfirst bearing means; a cover member secured in and closing off said openend of said housing, said cover member having a hole therein; resilientmeans interposed between said cover member and the opposite face of saiddisc, said resilient member being pressed against said disc by saidcover so that said disc is clamped between said shoulder and saidresilient member; second bearing means mounted in said hole, a secondportion of said shaft rotatably supported *by said second bearing means;means mounted within said hole for loading said second bearing means andurging said shaft towards said first bearing means so as to also loadsaid first bearing means; and a depressor assembly secured to said shaftand including a depressor member spaced radially away from said shaft,said depressor member disposed so as to press successive portions ofsaid diaphragm into contact with successive portions of said at leastone conductive element as said shaft is rotated relative to saidhousing.

12. An electrical device as defined by claim 11 wherein said end wallhas an opening located in alignment with said hole, and further whereinsaid first bearing means is mounted in said opening.

13. An electrical device as defined by claim 12 wherein said shaftprojects out of said end wall.

14. An electrical device as defined by claim 11 wherein said covermember includes terminal means for said diaphragm and also said at leastone electrically conductive element, and flexible conductive meansconnecting said terminal means with said diaphragm and said at least oneelectrically conductive element.

References Cited UNITED STATES PATENTS 2,862,088 11/1958 Mairs 338-1542,916,717 12/1959 Hartman et al. 338-154 2,917,720 12/1959 Budd et al.338-454 3,070,768 12/1962 Mairs 338154 3,102,989 9/1963 Sielsch 338l543,198,895 8/1965 Richman ZOO-11 X 3,274,350 9/1966 Mongeau 200-11 ROBERTK. SCI-IAEFER, Primary Examiner.

H. J. HOHAUSER, Assistant Examiner.

